I would 100% follow exactly what Pullrite says. I say that from a bad experience with them. Back in 2005-06 I had a hitch like yours, used the recommended silicone. Ended up with some major galling and head seperation.
This happened to one of my good work buddies. His hitch dealer/installer told him a certain lube to use. The dealer was at fault as he didn't keep current on all the lube changes from Pullrite.
Anyhow the hitch slide part bound up and some how forced the jaws to open just as he made a right turn on to a state hiway. Result was the trailer took the tail gate off his new '08 2500 chevy and the 5er landed in the middle of the intersection.
Pullrite gave him a whole new hitch and the dealers insurance paid for the trailer repair.
OP....
As many lube changes and material changes as the Superglide has gone through I would sure use Pullrites 1-800 number and find out which lube they recommend for a specific year model hitch.